Distillation vapor and feed mixing process

ABSTRACT

The present invention is a distillation vapor and feed mixing and subsequent separation process and apparatus involving the introduction of a vaporizing liquid feed into a flash zone via a tangential nozzle into a mixing and separation chamber which directs the feed into a circumferential path to enhance mixing, and the redirection of rising vapors from the distillation below the flash zone by baffling these vapors into the chamber inlet. The rising vapors are inspirated by the high velocity feed at the inlet side of the chamber and intimate contact and mixing of the rising vapors with the vaporizing feed are enhanced by creating a spinning action. Preferably, the chamber runs peripherally and slightly downward along the inside wall of the distillation column along an arc no greater than 360°. Alternatively, the mixing section of the mixing and separation chamber may be located outside of the distillation tower and the feed, passing through a jet ejector would inspirate the rising vapors. Increasing contacting and mixing efficiency in a distillation flash zone increases the yield of more valuable overhead product for the same energy input or permits lower energy input for constant separation between overheads and bottoms in the flash zone.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improved efficiency of mixing andsubsequent separation of distillation rising vapors with input feed andin most cases, to achieve lower partial pressure for vaporizing morefeed entering the flash zone to increase the yield of more valuablelighter products for constant energy input; or, conversely, reduceenergy input for constant yield. It is directed toward a process and anapparatus which involves the use of a mixing and separation chamber atthe feed nozzle of the distillation column. The process and apparatusare applicable to any distillation process but are particularly usefulin crude oil distillation, primary and secondary distillation.

2. Prior Art Statement

Historically, in a distillation process, a vaporizing feedstock has beenfed into the distillation column at what is called the "flash zone" bypressurized injection, typically through a feed flush or tangentialnozzle which merely sprayed or otherwise injected the vaporizing feedout over the rising vapors from the fractionation or stripping sectionlocated below the flash zone. While this technique was used for a longtime and distillation was achieved, it was recognized that much of thehot liquid feed remained as droplets and not all of the feed madecontact with all of the rising vapors. The actual efficiency of mixingand contacting the rising vapors with the vaporizing feed was impairedand excessive amounts of the heavy liquid fractions were carried upwardto fractionation sections above the flash zone.

Subsequently, it was discovered that the liquid droplets could be moreefficiently separated from the feed vapors by introducing the feedthrough a tangential feed nozzle into an open bottom chamber or bafflewhich was circumferential. Advantageously, an open bottom chamber wasdownwardly sloped and did not make a complete turn within thedistillation column. It is recognized that the centrifugal motion of thehot feed and the outward (and slightly downward) turbulent spray of thevaporizing feed into the rising vapors coalesced the droplets so thatfewer liquid drops are entrained and carried above the flash zone. Whilethis prior art improvement somewhat enhanced the separation of liquiddroplets from the rising vapors and feed vapors, it forced most of thedroplets to follow the circumferential wall of the flash zone, and didnot fully address the problem of large portions of the liquid feedseparating from its own forming feed vapors before those feed liquid andvapors mixed with the rising vapors and this resulted in poor contact.Thus, the improved system decreased entrainment of rising droplets butdidn't eliminate, and possibly magnified, the problems of "falling"liquid feed and inefficient mixture of feed liquid and vapors withrising vapors from the stripping section below the flash zone.

BRIEF SUMMARY OF THE INVENTION

The present invention is a distillation vapor and feed mixing andseparation process and an apparatus involving the introduction of avaporizing feed to enhance their contacting, mixing and separation withthe rising vapors to the flash zone. All of the rising vapors are mixedwith the hot feed in a special mixing and separation chamber, therebyminimizing prior art problems while enhancing the mixing and contactingefficiencies of the rising vapors and the feed. Maximizing the mixingefficiency of the rising vapors with the vaporizing feed results in agreater partial pressure reduction on the vaporizing feed to increasethe quantity of feed vaporized. This increases the yield of morevaluable overhead product for the same energy input to the flash zone.For example, in a primary crude distillation flash zone, for constantenergy input, calculations show that the increased yield of morevaluable products may be increased, for example, by at least 2 percent.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is more fully understood and variations encompassed by thepresent invention may be seen in light of the following detaileddescription of the invention, taken in conjunction with the drawings,wherein:

FIG. 1 represents a cut oblique view of a distillation column using afeed chamber of the prior art;

FIG. 2 shows a schematic front cut view of the FIG. 1 prior art device;

FIG. 3 illustrates a cut oblique view of one embodiment of adistillation column using a mixing chamber and rising vapor baffle ofthe present invention;

FIG. 4 shows a schematic front cut view of the present invention deviceof FIG. 3;

FIG. 5 illustrates a schematic front cut view of another embodiment ofthe device of the present invention; and,

FIG. 6 shows a top view of the device shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, distillation column 1 is shown with hot liquidfeed 3 entering nozzle 5. Nozzle 5 is shown tangentially arranged withrespect to column 1 (although flush nozzles or other angles aresometimes used). The particular column 1 shown here is circular incross-section, although other configurations such as conical orhexagonal could be used. Also, the column 1 could be for anydistillation, stripping, fractionating or other gas-liquid separationcolumn, and thus, the term "distillation column" as used herein shouldbe accordingly broadly construed. Column 1, for purposes ofillustration, is a section of a primary crude oil distillation column,although it could be a primary fractionation following a catalyticcracking, steam reforming or other process, or a secondary or vacuumdistillation column.

Stripping section 7 with trays 29 has rising vapor 9, e.g. distillationvapor or steam-rich vapor (contains hydrocarbon vapors stripped from thebottoms product), passing upwardly therethrough and into the lower partof the flash zone 11. It then passes into the upper part of the flashzone 13 and into the upper fractionating area, as is well recognized inthe art.

Prior art vaporizing feed chamber 15 is shown and makes a perpheral turninside the column 1 and along its perimeter for an arc distance lessthan a full turn. Prior art vaporizing feedchamber 15 has top portion17, and side walls 19 and 21 and has no bottom. Vaporizing feed chamber15 is connected to nozzle 5 via port 16 and has an open downstream end27 within the lower part of the flash zone 11. Typically, feed 3 entersfeed chamber 15 circumferentially and is directed slightly downwardly ina swirling manner primarily to minimize the entrainment of liquiddroplets in the vapors leaving upward from the lower part of the flashzone 11. Centrifugal action forces a large percentage of the heavierliquid feed droplets to follow the inside wall of the flash zone and,thus, the liquid flowing on the wall does not mix with all of the risingvapors passing upward in the center of the flash zone.

FIG. 2 shows a frontal cut schematic view of the prior art apparatus ofFIG. 1, with like parts like numbered.

FIG. 3 illustrates one prefered embodiment of the present invention.Shown is distillation column 31 with flash zone 33 and stripping zone35. Also shown are mixing and separation chamber 37 and partition baffle39. Tangential nozzle 41 is shown wherein vaporizing feed 43 is fed intocolumn 31 via nozzle 41 and mixing and separation chamber 37 and intoflash zone 33. Chamber 37 has a port 55 at its upstream end and an opendownstream end 53. It also has a top portion 45, side portions 47 and 49and a bottom portion 51. Mixing and separation chamber 37 has, in thisexample, a rectangular cross-section. However, it could be of a circularcross-section, i.e. tubular, or otherwise, and is generally sloped, as amatter of design, so that efficient flow and mixing are achieved.

Bottom portion 51 could be the same length as top and side portions 45,47 and 49, and advantageously is shorter in length so that the opendownstream end 53 of mixing and separation chamber 37 has an open ordropped out bottom. This enhances more flashing of the feed 43 becauseof more complete mixing with rising vapors 57. In this case, risingvapors 57 flow out of stripping section 35 and are redirected intochamber 37 by partition baffle 39 and the connecting tube section 59 ofpartition baffle 39. All of rising vapors 57 move upward from strippingsection 35 and trays 63, along the bottom of partition baffle 39 and upits tube section 59 into the upstream end of chamber 37. The vaporsenter the chamber from the bottom through port 60 where a deflectorbaffle 64 is used to accelerate the feed 43 to have a jetting action forinspirating the rising vapors 57. The deflector baffle 64 is also usedto direct the liquid feed droplets in a spinning motion to increasemixing of feed with rising vapors. Feed 43 and rising vapors 57 mixvigorously as they flow together in a swirling fashion through chamber37, and out of chamber 37's open downstream end 53 to flash zone 33,where the liquid gravitates to the bottoms product stripper tray 63, andthe vapors pass upward to the fractionation areas above the flash zone.Thus, the rising vapors are directed to the inlet side or bottom of thepresent invention apparatus which incorporates baffles in an eductionpromoting arrangement plus a chamber which directs the feed plusdistillation vapor mixture into a circumferential and/or toroidal pathto enhance mixing and promote intimate contact of the feed anddistillation rising vapors and achieve the lowest partial pressure forthe vaporizing feed before separating resultant liquid and vapors whilealso retaining the coalescing of liquid droplets and spray so as tominimize entrainment of the heavier fractions above the flash zone.

A front cut schematic view of the apparatus and process of FIG. 3 isshown in FIG. 4 wherein like parts are like numbered. In general, themixing and separation chamber used in the apparatus and process of thepresent invention is as described above and below, and is advantageouslyarcuated less than 360° of circumference in length, especially between90° and 270° in length. The bottom portion of the mixing and separationchamber may be the same length or shorter than the length of thechamber, and is preferably shorter, e.g. 40° to 200° in length.Preferably, the mixing and separation chamber is oriented slightlydownwardly from its upstream end to its downstream end. Although shownrectangular in cross-section, the chamber could be circular or oval toenhance the spinning.

To enhance liquid separation and flow to the stripping section 35 whilepreventing vapor bypassing of the mixing zone, a downcomer 61 should beinstalled at the bottom of partition baffle 39. To further enhancesealing of this downcomer, it may be desirable to install an inlet weir62 on the top of stripping tray 63.

FIGS. 5 and 6 show cut side and cut top views of an alternativeembodiment of the present invention apparatus. Distillation column 71 isshown in part and contains flash zone 73 and stripping section 75 (traysnot shown). Mixing and separation chamber 77, feed nozzle 65 andpartition baffle 67 work together to enhance complete contacting of therising vapors 74 and 76 and the liquid feed 78. Feed nozzle 65 (FIG. 6)is connected to mixing and separation chamber 77, and vaporizing liquidfeed 78 passes into nozzle 65 and then into chamber 77 as shown. Atchamber 77's open upstream end 99 is rising vapors inlet 97 withdeflection baffle 95. The deflection baffle 95 may be designed toprovide a jetting and spinning action from the high velocity feed 78 toinsprirate the rising vapors 76. Also included in the mixing zone is asecond deflection baffle 98 to create a spinning action in chamber 77.Partition baffle 67 physically divides most of the distillation column71 at the bottom of flash zone 73 as shown. In this embodiment,partition baffle 67 includes a component which has an upwardly slopedrestricted section 93 that is connected to rising vapors inlet 97 ofchamber 77. Thus, vapors 74 which rise up from stripping section 75 areredirected to rising vapors inlet 97 (rising vapors 76) due to theconfiguration of partition baffle 67. In chamber 77, rising vapors 76contact and mix intimately with vaporizing liquid feed 78 and themixture 88 passes to the separation section 79 of chamber 77 to opendownstream end 101 where the flashed mixture enters flash zone 73 withits vapors rising to fractionation sections (not shown) located aboveflash zone 73 as characterized by flash zone vapors 85. Mixing section92 of chamber 77 has a bottom 91 which is preferably shorter in lengththan the mixing and separation chamber 77, and mixture 88, therefore,initially separates in section 79 where the most of vapors enter intoflash zone 73 as examplified by flow arrows 80, 81 and 82. A largeportion of the liquid which is not "flashed" swirls around the innerflash zone wall to fall down into stripping section 75 as examplified byflow arrow 84. This liquid enters a downcomer seal system noted in FIGS.3 and 4, and are shown here as downcomer 70 and inlet weir 72. Thesefunction in the same manner as downcomer 61 and inlet weir 62 shown inFIGS. 3 and 4.

This is one of several physical arrangements that can be used tosegregate the rising stripper vapors and introduce them into the mixingand separation chamber with the vaporizing feed. For instance, aninverted conical baffle can be used to collect the vapors above thestripper and funnel them into a pipe that curves in the flash zone todischarge the vapors at the mixing chamber inlet. Alternatively, thepipe could be eliminated and a flat or curved baffle could be connecteddirectly to the mixing and separation chamber to acheive the desiredresult.

Although normally less attractive, certain situations may justifylocating the mixing chamber externally from the tower, e.g. outside ofthe flash zone. For example, referring to FIG. 3, pipe 59 containing therising vapors 57 would pass through the distillation column wall 31 andjoin the vaporizing feed 42 before the tangential nozzle 41. An eductoror jet ejector could be used to inspirate the vapors 57 into the feed.The resultant mixture would then pass into the tower through atangential separation chamber having a top portion 45 and side portions47 and 49 and no bottom portion. Thus, in all embodiments, the mixingand separation chamber is at least partially located within the tower,and preferably entirely within the tower as discussed above.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. In a distillation process wherein vaporizingliquid feed is being fed into a flash zone located within a column andcontacted with rising vapors from the stripping section therein animprovement, for more complete mixing of the vaporizing liquid feed withthe rising vapors from the stripping section in order to achieve a lowerpartial pressure effect on the feed to improve overallfractionation-energy efficiency, to minimize entrainment of heavy liquiddropleets in vapors leaving the flash zone, and, to improve the flow ofliquid on the top stripping tray, which improvement comprises:(a)introducing the vaporizing liquid into the flash zone located within thecolumn at an angle approximately tangential to the column via a nozzleand through a mixing and separation chamber having a port at itsupstream end at the nozzle and an open downstream end at the flash zone,said chamber being constructed to approximately conform to the insidecross-sectional configuration of the column at the flash zone, andhaving side walls, a bottom and a top and having a rising vapors inletport near the upstream end, said chamber having a length which is lessthan the full perimeter of the column at the flash zone; (b) enhancingthe efficiency of the contacting and mixing of all of the rising vaporswith the vaporizing liquid feed by redirecting all of the rising vaporsfrom the column into said chamber near its upstream end by physicallypartitioning at least a part of the column with a partition bafflelocated in the flash zone to direct the rising vapors to the risingvapors inlet of said chamber; and, (c) further enhancing the efficiencyof the contacting and mixing of all of the rising vapors with thevaporizing liquid feed by creating a spinning action with a deflectorbaffle located at said rising vapors inlet whereby high velocity feedinspirates all of the rising vapors so as to create the spinning actionin said chamber and so as to thereby effect intimate mixing of allrising vapors from the stripping section with the vaporizing liquidfeed.
 2. The process of claim 1 wherein the column is circular in itscross-sectional configuration at the flash zone and said chamber isarcuated and makes an arc of less than 360° and is oriented slightlydownward from its upstream end to its downstream end.
 3. The process ofclaim 2 wherein said chamber makes an arc of between 60° and 270°. 4.The process of claim 3 wherein the bottom of said chamber makes an arcof between 40° and 200°.
 5. The process of claim 1 wherein thedistillation process is a primary atmospheric distillation process. 6.The process of claim 1 wherein the distillation process is a secondaryvacuum distillation process.
 7. The process of claim 1 wherein thedistillation is crude oil distillation, the vaporizing liquid feed iscrude oil and the rising vapors are steam-rich bottoms hydrocarbonvapors.
 8. The process of claim 7 wherein the column is circular in itscross-sectional configuration at the flash zone and said chamber isarcuated and makes an arc of less than 360°.
 9. The process of claim 8wherein said chamber makes an arc of between 60° and 270° and isoriented slightly downward from its upstream end to its downstream end.10. The process of claim 9 wherein the bottom of said chamber makes anarc of between 40° and 200°.